This invention relates to an activated sludge sewage disposal system and more particularly to such a system specially adapted for marine use. Reference may be made to the aforementioned application for a discussion of various prior art systems of this nature.
Problems encountered with prior art equipment such as disclosed in the aforementioned patent application, include surging of fluid from the aeration chamber to the settling tank when displacement of fluid in the aeration chamber increases the head of fluid at the standpipe. Such surging may occur when the ship rolls or pitches or both, depending on the location of the sewage disposal apparatus relative to the ship. Surging will tend to carry unmacerated solids into the pond in the settling tank, overloading the skimmer and sludge return.
In the apparatus of the aforementioned patent application, although manually controlled valve means in the top of the settling tank enables all the air in the top of the tank to be vented to atmosphere when the apparatus is first started up and the tank is flooded with effluent from the aeration chamber, during normal operation of the apparatus any gas entrained by the effluent will collect at the top of the pond in the top of the settling tank. The gas may increase in volume to the point where the gas-effluent interface is below the level of the skimmers, rendering the skimmers inactive. Even without lowering of the interface to such an extreme degree, gas at the top of the pond will tend to concentrate over the top of each skimmer and reduce its efficiency.
A further problem with the skimmers of the apparatus of the aforementioned application is the presence of dead areas at the top of the pond where the skimmer action is ineffective to create surface movement sufficient to draw in floating sludge to the skimmer outlet, resulting in the buildup of sludge cake in the top of the pond which ultimately may block the skimmer means from functioning.